Method of coating continuous sodium silicate fibers



METHOD OF COATING commuous SODIUM SILICATE FIBERS H. l. GLASER OriginalFiled July 28. 1961 Aug. 9, 1966 INVENTOR. HELLM T 1'. 61/1551? BY m u dJrrapwvs Patented August 9, 1966 3 Claims. (Cl. 65-3) This is a divisionof Serial Number 128,351, filed July 28, 1961, now abandoned.

The present invention relates to siliceous fibers and particularly tocontinuous sodium silicate fibers and methods for the productionthereof.

In recent years, expanding demands for insulating or reinforcingmaterials which will withstand extreme conditions of temperature haveled to a widespread utilization of silica fibers which will enduretemperatures from 300 F. to +3000 F. To date, the most practical methodfor the preparation of such fibers has comprised the leaching ofconventional glass fibers such as those fibers formed of an E glasscomposition. In this approach, a fiber consisting essentially of silicais obtained by extracting through leaching the monovalent, divalent andtrivalent glass forming metal constituents. The fiber remaining afterleaching may comprise as much as 99.9% by weight of silica. Suchleaching is conventionally achieved by submerging the glass fibers ineither an inorganic or organic acid and the leaching elfe-ct may beaccelerated by simultaneously heating the leaching bath. This method isamply disclosed by US. 2,215,039, 2,221,- 709, 2,461,841, 2,491,761,2,500,092, 2,624,658, 2,635,- 390, 2,686,954, 2,718,461 and 2,730,475.

However, the attainment of fibers possessing a high silica content bymeans of the described technique is attended by serious drawbacks. Notonly is the process subject to large material losses in respect to thehighpercentage of metal oxides which are removed from the glass andwhich in the case of most fiberizable glasses such as E glass compriseapproximately 40 to 50% by weight of the fiber, but in addition theresultant leached products undergo severe shrinking. The latter problemis particularly pronounced in the case of leached products comprisingcontinuous fibers in the form of fabrics, roving and the like. At thesame time, such continuous fiber products are particularly desirabledueto their suitability for reinforcing applications such as filamentwinding and fabric or roving reinforcements such as lay-ups, pre pregs,chopped roving and the like.

While an apparent solution to the shrinkage problem lies in theutilization of fibers having a higher silica content which consequentlysuffer a smaller weight loss. upon leaching, this solution is notreadily susceptible to reduction to practice. This. situation stems fromthe fact that fibers having a high silica content, such as sodiumsilicate fibers, are rapidly degraded by moisture attack at atmosphericconditions, are extremely friable, and to date have not been amenable tocommercial production in a continuous filament form.

It is an object of the present invention to provide continuous sodiumsilicate fibers.

A further object is the provision of durable sodium silicate fibers.

Another object is the provision of methods for the fabrication ofcontinuous sodium silicate fibers.

An additional object is the provision of a batch composition from whichcontinuous sodium silicate fibers may be attenuated.

Still another object is the provision of protective size compositionsfor sodium silicate fibers.

A still further object is the provision of silica fibers free fromshrinkage upon leaching.

These and other objects and advantages of the invention will be moreclearly explained and developed in the subsequent detailed descriptionand in reference to the attached drawing which depicts a schematic viewof a preferred method and apparatus for the melting, attenuating,coating and winding of the continuous sodium silicate fibers of theinvention.

The foregoing objects are achieved by means of melting a batchcomposition comprising materials which yield at least by weight ofsilica upon fusion, flowing the resultant molten material throughorifices provided in a fiber forming bushing to form filaments,attenuating the filaments to form continuous fibers andimmediatelycoating the fibers with a protective medium which serves toprevent moisture inspired degradation.

Batch composition Ingredient: Percent by weight sio 69.6 Na SO 2.0 Na CO28.4

Any batch which yields fibers comprising 75% by weight or more of silicawill also yield a satisfactory continuously fiberizable melt and fiberswhich do not undergo severe shrinkage upon leaching. In the melting ofthe above batch composition, the sulfates and carbonates are vaporizedand dispelled to yield fibers comprising approximately by weight ofsilica and 20% by weight of sodium oxide. The batch employed may beformulated to utilize or include metallic oxide fluxes or combinationsof metallic oxides in addition to or in place of sodium oxides such asthe oxides of lithium, potassium and boron, and the ratio of oxides oroxideforming metal compounds to silica may be decreased to yield ahigher silica contentwhen appropriate melting conditions and refractoryoralloy bushings of adequate heat and erosion'resistance are employedwith conventional platinum bushings. However, if batches having a highermelting temperature are utilized, refractory or alloy materials havinghigher temperature and erosion resistance such as rhodium, may beemployed in the fabrication of the bushing or melting tank.

F iberization The fibers of the invention are formed by methods andapparatus which are conventional in the formation of glass fibers suchas fibers formed from E glass and the fiber forming rate and yield isapproximately the same as in the case of E glass fibers. For example, ayield of approximately 30 pounds of fibers per hour is obtained whenfibers having a diameter of approximately 0.00035 to 0.00038 inch areattenuated from a conventional textile bushing provided with 408 fiberforming orifices. In

3 tinuous fibers 15 and wound into a cylindrical package form 16.

While the drawing represents a simplified or basic form of theinvention, it should be realized that the molten material 13 containedby the melting section of the tank 11, may be fed to a plurality ofbushing tips 14 in order to provide a multiple forming arrangementcomprising a central or common melter and a plurality of fiber-formingbushings.

With the depicted structure and the preferred batch composition, thebatch is melted at a temperature between 2700 and 2800 F. in the region17 where melting is achieved, and reaches the bushing tip section 14 ata temperature of approximately 2300 to 2400 F.

The heating means may also be widely varied and when a melterconstructed entirely of platinum or a metal alloy is employed, integralportions of the melter may be utilized as electric current carryingmembers which generate the requisite heat. Alternatively, when arefractory or metal coated refractory material is em ployed in thefabrication of the bushing, other conventional heating means such as gascombustion may be utilized.

Forming size compositions As previously stated, the fibers of theinvention are subject to extensive attrition as the result of moisturedegradation, if exposed to atmospheric conditions for even short periodsof time. Consequently, a protective coating or film is applied to thefibers immediately subsequent to their formation, as shown by thedrawing wherein the continuous fibers 15 are brought into contact with atransfer roll 18 which is supplied with the coating material by means ofa reservoir 19.

While a graphite transfer roll 18 is the preferred applicator, otherconventional contact, immersion or spray application methods andapparatus such as the apron applicator disclosed by US. 2,873,718, padapplicators as shown by US. 2,390,370, 2,744,563 and 2,778,764, spraysas disclosed by 2,491,889, 2,846,348 and 2,906,470, or other types oftransfer rolls such as those disclosed by US. 2,693,429 and 2,742,737,may also be utilized.

. New and unusual size compositions are also necessary to achieve thegoals of the invention. To produce a satisfactorily durable andleachable fiber, a size composition which provides a continuous anduniform protective film capable of withstanding both moisture attack andthe rigors of basic processing is required. In addition, the sizecomposition must be applied in a substantially anhydrous form due to thedeleterious effect of water upon the fibers. Furthermore, the sizecomposition must be readily removable when the end use of the fibersentails leaching. In such instances, efiicient processing requires thatthe protective coating be capable of ready removal by exposure tothermal conditions below the melting or softening point of the fibers,or by washing in a solvent or bath which decomposes, dispels or removesthe size composition. While the size composition might be removed duringactual leaching if a material soluble in or removable by the leachingcomposition is employed, it has been found that the deposition orprecipitation of the ingredients of this size composition in theleaching medium serves to neutralize the leaching power of the mediumand the necessity for removing such deposits or precipitates renders theprocess uneconomical. Accordingly, when leaching is contemplated themost desirable coating materials are those which may be easily andeconomically removed from the fibers prior to the leaching step. Whenthe processing of the fibers does not entail leaching, a coat-ing orsize composition comprising a solution of a synthetic resin in ananhydrous solvent serves to yield durable fibers.

The preferred coating materials or forming size compositions of theinvention comprise solutions of cereous compositions in anhydroussolvents. Such materials yield continuous protective films due to thesolvent system which is employed as contrasted to conventional formingsizes which comprise aqueous emulsions of resinous particles. Stillfurther, the sizes of the invention are readily removable by mildthermal, solvent or washing treatments and are preferably removed bymeans of immersion in a dilute acidic bath.

The term cereous as employed throughout the specification and claims isintended to connote, designate and encompass all true waxes and wax-likematerials which are soluble in anhydrous solvents. This designationincludes the esters of mono-, diand polyhydroxy alcohols as well asfatty acids per se, alcohols, and higher hydrocarbons which are of awax-like nature. Thus, in addition to true waxes comprising non-glycerylesters formed from monohydroxy alcohols, the definition also includesthe glycerol or polyhydroxy esters of fats and oils, natural waxes ofplant or animal origin such as beeswax, scale insect waxes, wool,sperm-aceti, marine waxes, palm, candelilla, flax, cotton, sugar cane,Japan, myrtle and cranberry waxes; fossil, mineral, earth and lignitewaxes such as algae, Utah, ozocerite, Montan, peat, brown coal andceresin waxes; petroleum or hydrocarbon waxes such as paraffin,petrolatum, crystalline and micro-crystalline waxes; synthetic waxessuch as the phthalimides, chlorinated and stearamide waxes; and thefatty acids per se.

While stearic acid is a preferred coating material, other fatty or waxyacids such as oleic, palmitic, linoleic, linolenic, butyric, caproic,caprylic, capr-ic, lauric, myristic, anachidic behenic, erucic, andclupanodonic acid also yield highly satisfactory results, In selectingthe cereous material to be employed, heed must also be paid to the easewith which it may be removed. For example,the elevated melting points ofsome of the microcrystalline waxes render them less susceptible tothermal removal than a material such as paraffin.

While 1,1,l-trichloroethane is a preferred solvent when stearic acid isemployed as the solute, other solvents such as diacetone alcohol, carbontetrachloride and the like are also operable. The 1,1,1-trichloroethaneis preferred because of the fact that it possesses a flash pointconsiderably above most similar solvents. This is an important factorbecause of the fact that coating is accomplished in close proximity tothe high temperature fiber forming bushing or feeder and flammabilityand volatility are important considerations unless a thorough exhaustingor ventilation of the forming area is practiced. In the event thathighly flammable or toxic solvents are utilized in conjunction with theexhausting of the volatil ized solvent, solvent recovery may also beconducted in order to improve the economics of the operation. Generally,the choice of the solvent will depend in great part upon a number offactors including the solubility characteristics of the solute selected,the hazards entailed in the utilization of the solvent, and the effectof the solvent upon the removal characteristics of the film if leachingis contemplated.

When the preferred formulation comprising stearic acid1,1,l-trichloroethane is utilized, the ingredients are preferablyemployed in the following proportional ranges which are expressed inpercentages by weight:

Percent Stearic acid 225 1,1,1-trichloroethane 75-98 A preferredformulation comprises:

Stearic acid 7 1,1,1-trichloroethane 93 If the strands of the inventionare to be immediately twisted the above formulation is adequate.However, if storage prior to twisting is contemplated, the inclusion ofa plasticizer in the formulation is advisable to prevent undue stiffnessof the strands. Camphor has proved highly efiicient in the plasticizerrole. However, even with the use of a plasticizer some protection of theforming packages is desirable in order to retard the volatilization ofthe plasticizer, ethylene bags has provided an adequate solution.

The efficacy of the size compositions of the invention is demonstratednot only by the fact that they make possible a practical process for theproduction of continuous sodium silicate fiber, but also by thedurability of the product which is yielded. When such fibers werefabricated with a protective coating comprising an emulsion of asynthetic resin, the fibers were completely unprocessable. With a matterof hours the fibers became so friable as to be incapable of removal fromthe wound cylindrical package and shortly thereafter the mere act ofdropping the package resulted in the splitting of the fibers throughtheir entire mass which had by then become an integral structure ratherthan grouped, adjacent fibers and strands. In contrast, a Wound packageof the sized fibers of the invention may be completely submerged inWater for a period of 24 hours, and upon removal therefrom the strandmay be readily unwound from the package.

In addition, the size compositions of the invention may be readilyremoved from the surfaces of the fibers and strands by means ofimmersion in a hot, dilute bath of sulfuric acid or by a thermaltreatment at 400 F. to provide an unprotected, leachable medium.

The strength and durability of the products of the invention is alsoaptly demonstrated by the fact that strands comprising a plurality ofthe fibers were twisted and woven into fabrics without undue difiiculty.Not only was such processing impossible with previous sodium silicatefibers, but also the fabrics thus provided by the invention yield up onleaching, an ideal reinforcing medium for structures which are exposedto extreme temperatures such as rocket nose cones and the like. Inaddition, minimal shrinkage is experienced upon leaching. Further proofof the strength and durability of the fibers is provided by thefollowing table which sets forth the tensile strengths of 27 fibersformed in accordance with the present invention:

Breaking Load (grams) Breaking Stress (lbs/sq. in.)

. Fiber N o.

Average Storage of the forming packages in poly- While the fibers of theinvention are primarily intended as leachable and processableintermediates to be employed as reinforcements or insulation forapplications which experience extreme conditions of temperature, .theymay also be employed in electrical or optical applications since theirelectrical and optical characteristics are very similar to those ofquartz fibers. Consequently, oriented light may be transmitted throughone or more of the fibers of the invention. In applications which do notentail leaching, a more durable size composition in the form of ananhydrous resinous solution may be desirable. For example, solutionscomprising 2l5% by weight of epoxy resins in 90% by weight of diacetonealcohol or trichloroethane have yielded fibers of excellent durability.Coatings of the latter type are not desirable upon fibers to besubjected to leaching however, due to the difficulty involved inremoving such coatings either before or during leaching.

It is apparent that novel fibers and methods for their formation andsizing as well as unusual leached structures and size compositions areprovided by the present inventlon.

It is further obvious that various changes, alterations andsubstitutions may be made in the compositions, methods and products ofthe present invention Without departing from the spirit of the inventionas defined by the following claims.

I claim:

ll. A method for preparing silicate fibers comprising melting a batchcomposition consisting essentially of silicon compounds and compounds ofmetals selected from the group consisting of sodium, lithium, potassiumand boron, flowing the resultant molten mass through orifices to formfilaments comprising at least 75% by weight of silica and an oxide of ametal selected from the group consisting of sodium, iithiurn, potassiumand boron, continuously attenuating said filaments and applying ananhydrous solution of a cereous material as a protective sizecomposition to the sunfaces of said filaments.

2. A method as described in claim 1 in Which said protective sizecomposition comprises an anhydrous solution of a fatty acid.

3. A method as described in claim 1 in which said protective sizecomposition comprises between 2 to 25% by Weight of stearic acid andbetween 75 to 98% by weight of 1,1,1-trichloroethane.

References Cited by the Examiner Textbook of Glass Technology, published1925, Hodkin et 211., published by D. Van Nostrand Co., New York, NY.(p. 87-93 and p. relied on).

DONALL H. SYLVESTER, Primary Examiner.

R. LINDSAY, Assistant Examiner.

1. A METHOD FOR PREPARING SILICATE FIBERS COMPRISING MELTING A BATCHCOMPOSITION CONSISTING ESSENTIALLY OF SILICON COMOUNDS AND COMPOUNDS OFMETALS SELECTED FROM THE GROUP CONSISTING OF SODIUM, LITHIUM, POTASSIUMAND BORON, FLOWING THE RESLTANT MOLTEN MASS THROUGH ORIFICES TO FORMFILAMENTS COMPRISING AT LEAST 75% BY WEIGHT OF SILICA AND AN OXIDE OF AMETAL SELECTED FROM THE GROUP CONSISTING OF SODIUM, LITHIUM, POTASSIUMAND BORON, CONTINUOUSLY ATTENUATING SAID FILAMENTS AND APPLYING ANANHYDROUS SOLUTION OF A CEREOUS MATERIAL AS A PROTECTIVE SIZECOMPOSITION TO THE SURFACES OF SAID FILAMENTS.